The preparation of polyurethane-urea elastomers by reacting NCO semiprepolymers with mixtures of aromatic diamines and higher-molecular compounds containing hydroxyl or amino groups is known and is described e.g. in U.S. Pat. No. 5,418,260 and EP-A 656 380. To achieve specific mechanical properties in the moldings produced therefrom, it is necessary to add reinforcing agents to the reactants, especially in order to improve thermomechanical properties and substantially increase the flexural modulus. For such reinforced polyurethane-urea elastomers, which are used for the production of sheet moldings such as car wings, doors, rear flaps and sills, it is desirable for these parts to be easily releasable from the moulds in order to ensure the shortest possible cycle times by means of a quick-release system.
However, quick-release systems have the disadvantage of a low surface tension due to the release agents. The surface tensions here are only 34 mN/m, but a good lacquer adhesion requires surface tensions of 40-42 mN/m. Values around 42 mN/m may only be achieved by additional cleaning processes.